1. Field of the Invention
The present invention relates to an endoscope, and more particularly relates to an endoscope which has as an image pick-up device a plate like image sensor disposed within a viewing head thereof.
2. Description of the Prior Art
In addition to endoscopes having an optical fiber bundle as its image guide means, there have been proposed TV endoscopes of a type having as an image pick-up device an image sensor such as a charge coupled device (CCD) which comprises a great number of small photosensitive elements (pixels) arranged in matrix. Such TV endoscopes, which are far better than endoscopes heretofore used in terms of durability, the effect of video signal management and production cost, are still in the developmental stage.
In developing the TV endoscope, there are two objectives the first objective being to reduce the outer diameter of the endoscope to allow insertion of it into a cavity of a living body and the other requirement to improve the resolving-power i.e. increasing the number of picture elements on the image sensor. Accordingly, it becomes very important to efficiently arrange construction of the forward end section of the endoscope, particularly, the image sensor, or an objective lens assembly to make an optical image focus at the image sensor.
The inventor having as his objective the provision of a plate-shaped image sensor, has proposed an arrangement wherein: the plate-shaped image sensor is provided on a plane incorporating the center axis of the endoscope in the longitudinal direction; an objective lens assembly is disposed on one side of the plate-shaped image sensor, with the axial line of the objective lens assembly being in parallel to the plate-shaped image sensor; a right-angled prism is provided in the rear of the objective lens assembly to turn the light path at 90.degree., and a light emitting surface is cemented to the image sensor. With this arrangement, it has become possible to effectively utilize the outer diameter of the endoscope so as to provide an image sensor which is wide in width in the forward end portion having a small diameter.
Now, in order to observe an affected portion with the objective lens assembly, it is necessary to irradiate the affected portion by use of light guides. Because of this, light guides each formed on an optical fiber bundle or the like are provided on opposite sides of the objective lens assembly in parallel thereto in the forward end portion of the endoscope. In other words, the light guides are disposed close to a light receiving surface of the image sensor. It is possible that the light of the optical fiber bundle forming the light guide could leak to the light receiving surface of the image sensor. If any light other than the light from the objective lens assembly enters an image area forming the image pick-up area of the image sensor, then image pick-up function is hampered. If any light other than the light relating to the image formation enters a storage area acting as an image transferring area, then the transferring function is hampered. As the result, an accurate image may not be obtained or an image may be blurred due to a cause of blooming or the like.